The present invention relates to a plug valve. More particularly, the invention relates to a plug valve having a number of booster springs for biasing two opposing seal segments against a central plug in order to eliminate the float between the seal segments and the plug.
Prior art plug valves typically comprise a body which has separate inlet and outlet ports that are connected by a central cavity, a cylindrical plug member which is rotatably positioned between two semi-cylindrical seal segments that are mounted in the cavity, and a valve stem which is connected to both the plug member and an external handle. Each seal segment comprise a through bore which together with the inlet and outlet ports forms a flow passage through the body. In addition, the plug member comprises a transverse hole extending therethrough, and each seal segment forms a metal-to-metal circular seal with the plug member which is concentric with the flow passage. In operation, the plug member is rotatable between a valve open position, in which the hole is aligned with the flow passage, and a valve closed position, in which the hole is offset from the flow passage.
These prior art plug valves are usually designed to have a certain degree of clearance or xe2x80x9cfloatxe2x80x9d between the plug member and the seal segments, and the plug member is loosely mounted in the body so as to be able to drift between the seal segments during operation of the plug valve. This enables the pressure within the gate cavity to force the plug member into tight metal-to-metal sealing engagement against the downstream seal segment when the valve is in the closed position. However, in certain circumstances this float also allows the seal segments and the plug member to separate when the valve is in either the open or the closed position. When this happens, fine particles which are being conveyed through the plug valve can migrate between the seal segments and the plug member and consequently prevent the plug member from forming an effective metal-to-metal seal with the downstream seal segment when the valve is closed.
In accordance with the present invention, these and other disadvantages in the prior art are overcome by providing a plug valve having a body which includes an inlet port, an outlet port, and a cavity that is connected between the inlet and outlet ports; first and second seal segments which are mounted in the cavity and which each comprise a through bore which is coaxial with the inlet and outlet ports; the through bores and the inlet and outlet ports defining a flow passage through the body; a plug member which is rotatably positioned between the first and second seal segments and which includes a hole that extends transversely therethrough; wherein the plug member is rotatable between an open position in which the hole is aligned with the flow passage and a closed position in which the hole is offset from the flow passage; and a first booster spring which is positioned between the first seal segment and the body to bias the first seal segment against the plug member.
In a preferred embodiment of the invention, the plug valve includes first and second booster springs which are mounted in respective grooves that are formed in an outer face of the first seal segment. In yet another embodiment of the invention, the plug valve includes a third booster spring which is positioned between the second seal segment and the body to bias the second seal segment against the plug member. In still another embodiment of the invention, the plug valve includes third and fourth booster springs which are mounted in respective grooves that are formed in an outer face of the second seal segment.
In this manner, the booster springs will force the first and second seal segments against the plug member and thereby prevent fine particles from migrating between the seal segments and the plug member when the valve is in the open position. Consequently, the plug member will be able to form a clean, tight metal-to-metal seal with the downstream seal segment when the valve is closed.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings. In the drawings, the same reference numbers are used to denote similar components in the various embodiments.